Humans are constantly exposed to the vast mixture of chemicals that are present in the environment. Often this mixture contains both carcinogenic polycyclic aromatic hydrocarbons and other types of hydrocarbons and chemicals that have cocarcinogenic and/or tumor-promoting activity (i.e. urban air, cigarette smoke, etc.). To determine how combined exposure may influence the effects of carcinogens, the modifications induced by cocarcinogens and tumor promoters in the metabolic activation, detoxification, DNA interactions and biological effects of polycyclic aromatic hydrocarbons will be measured in hamster embryo cell cultures. The production of water-soluble glucuronic acid conjugates of hydrocarbon metabolites will also be measured and the role of these conjugates in the induction of biological effects by hydrocarbons will be investigated. The results obtained should aid in predicting the effects of exposure to carcinogenic chemicals in the presence of tumor promoters, cocarcinogens and mixtures of both, and, thereby, permit modification of these effects. The studies on glucuronic acid conjugate formation will help in interpreting the results of in vitro transformation assays when they are used to screen for carcinogens and may lead to the development of assays with enhanced sensitivity for the detection of carcinogens.